Electrical filter system



April 5, 1932 B. F. Mn-:ssNER 1,852,125

ELEC'IRICAI., FILTER SYSTEM Filed Jan. 8, 1929 'Patented Apr. s, 1932 UNITED KSTATES PATENT OFFICE :BENJAMIN F. MIESSNER, OF. SHORT HILLS, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, T RADIO CORPORATION OF AMERICA, 0F YORK,- N. Y., A CORPORA- ELECTRICAL FILTER SYSTEM Appueauon mea January s, 1929. serial No. 330,995.

i Another object is to employ, whe'n a system permits of the division of the direct current -component of the work current, opposing flux effects in filter coils to avoid excessive fluxl conditions tending to lessen in- -9 ductance values of such coils.

Theinvention will be understood by reference to the figures of the accompanying drawings in which like reference characters represent like parts so far as possible:

Fig. 1 diagrammatically illustrates a simle electrical'filter embodying my invention.

2 illustrates a modification of the arrangement of Fig. 1. Fig. 3 shows a filter arrangement including the feature of divided direct current components acting to reduce flux intensity in a filter coil.

In Fig. 1 the filter system is shown supplied from a SourceS with a periodically fluctuating current, such as a rectified alternating current or commutated direct `current. The filter system is shown to include aninductance coil L spanned by condensers C1 and C2, and is indicated as being connected to a workcircuit including load E, such as 40 the plate circuit or circuits of one or more three electrode vacuum tubes requiring direct current energizing for operation, as in a signal current amplifier. A condenser C3 may be connected across the source of supply S if desired as a storage capacity for supply energy and to aid'in smoothing out the supply current in cases where the energy demand isflarge, or where the fluctuations in the supply current are severe.l

5@ It will be noted that I connect the source S to the coil L at a point intermediate its ends, thus dividing coil L into two components L1 and L2, and the portion L,L forms an auxiliary alternating current circuit by way .of condenser C1. Because condenser C1 prevents flow of the direct current component in the auxiliary path including this condenser and the L1 portion of the coil, the direct current is directed into the work circuit including the load consuming element or elements E. However, fluctuating or alternating current .components tend to divide and flow in two directions in coil L, thus permitting choosing proper values of the L1 portion of the coil and capacity of condenser C1 with respect to L2 and C2 such that the alternating current component in portion L1 substantially neutralizes the alternating current component in portion' L2, thus leaving the current going to the load E substantially free from fluctuations.` Orany desired degree of fluctuations may be left in the working component of the current, as may be de- A sired under certain circumstances, as for example when fluctuation in a succeeding stage of an amplifier system is needed to buck or oppose fluctuation coming from a preceding stage.

I have in general chosen the coil portion L1 to beabout one quarter of the whole coil, and by making the capacity of condenser" C1 adequately large, a larger alternating current component tends to flow through the lower impedance path including these elements than the higher impedance path of the larger portion L2. condenser C and load E, thus making it possible to substantially eliminate the ripple or fluctuations across the load.

In Fig. 2 the source S is connected to one terminal of' the coil L and the load E is connected so as to divide the coil into two portions L1 and L2, the alternating current com- Ponent in L1 by wav of condenser C1 tending to neutralize the alternating current component in L2 as in the case of Fig. 1. The selection of the values of the elements in Fig. 2 is substantially the same as in the ca se of Fig. 1.

Consideration of the elements of Figs. l and 2, with an analysis of the inherent actions and reactions thereof when the system functions as described, explains the effectiveness of the system for the elimination of disturbing currents of the frequency especially desired to be eliminated with a small quantity of material. The auxiliary path includes condenser C1 and coil L1 very closely coupled to coil L2 through being wound on the same iron core, so that the mutual inductance between coils L1 and L2 is large compared to the inductance of coil Ll per see with the less than unity ratio between coils L1 and L2, I employ in this invention. The consequent large mutual inductance is effective in the auxiliary path, combining with the inductance of coil L1 to form the total effective inductance, but since the mutual inductance has no resistance component, the resistance is merely that of the smaller coil L1 inthe absence of an effective resistance component in the choice of a good quality condenser at C1. The larger the edective inductance of the auxiliary circuit, the less, and therefore more economical, can the capacity of condenser C1 be to eliminate disturbing currents or fiuctuations of a particular frequency, and this result I secure by not using a large inductance with corresponding high resistance, but/ with a small low resistance inductance supplemented by a larger mutual inductance 4substantially devoid of resistance component.

The arrangement of Fig. 3 is'particularly suitable where two loads E1 and E2 requiring different degrees of filtering are to be supplied. For example, the load lil2 may be the plate circuit .of the tube of the last stage of an amplifier and the load E1 the plate circuit of a preceding stage in the same amplifier. Because of the amplification which fluctuations in the preceding stage undergo on the way to the last stage it is particularly desirable that the current supplying the plate circuit of the preceding stage be highly filtered. Also, it may be that large fluctuations are desired in the last stage to neutralize amplified fluctuations coming from a preceding stage.

Fig. 3 only differs from Fig. 1 through having the load E2 connected from a point between the L1 portion of coil L and condendenser C1. The current for load E2 is filtered only by L1, C3 and C1, whereas the current for load E1 is additionally filtered by condenser C2 and has the advantage of the larger rtion L2 of coil L. However, as in the case of Fig. 1, the alternating current components in portions Ll and L2 oppose and act to reduce the fluctuating component ofthe current delivered to -both loads.

In addition to the opposing alternating current components Fig.l 3 provides for flux effects of two direct current components in coil L opposing each other, thus reducing the permanent fluit in the core of coil L to avoid any saturation effects adversely affecting the alternating current inductance of the coil. If4

the direct current load of E2 is larger than the direct current load of El, as is usually the case in amplifying systems, it is obvious that the larger current flowing through the smaller portion Ll is effective against a smaller current flowing through the larger porton L2 to.

more nearly equalize the opposing ampere turns of the two portions. This maintaining of large inductance is of importance to good filtering. I

I have found the filter arrangements herein described of' great assistance in eliminating hum ell'ects from radio receivers 'and like amplifiers employing three-electrode vacuum .tubes energized by the rectification and fltraf .ductance being connected between one terminal of said source and said-work circuit, a condenser connected between the other terminal o f said source and said tap, and condensers connected between said other terminal and each terminal'of said inducance whereby the alternating current component of the current flowing through said inductance is substantially neutralized.

2. In an electrical system, the combination of a source of rectified alternating current, a work circuit, and a filter system connected between said source and said work circuit, said filter system including an inductance divided into two sections with a ratio of atI least 2 to 1 by a tap, one section of said inductance being connected between one terminal of said source and said work circuit, a condenser connected between the other terminal of said sourcefand said tap, and condensers connected between said other terminal and each terminal of said inductance,

fone of, said condensers constituting a storage condenser for said source, whereby the alternating current component of the current flowing through said inductance is substantially neutralized. f

3. In an elctrical system, the combination of a source of rectified alternating current,ay

work circuit, and a filter system connected between said source and said work circuit, said filter system including an inductance divided into two unequal sections by 4a cap, the larger of said sections being connected between one terminal of said source and said work circuit, a condenser' connected between the other terminal of said source andsaid tap, Iand condensers connected between said other terminal and each terminal of said 1nductance, whereby the alternating current component of the current flowing through said inductance is substantially neutralized.

4. In an electrical system, the combination of a source of rectified alternating current, a work circuit, and a` filter system connected between said source and said work circuit, said filter system4 including an inductance divided into two unequalsections-by a tap, the larger of said sections being connected between one terminal of said source and said work circuit,` a storage condenser connected' through said smaller section to substantiallyT neutralize the field of the fluctuating current flowing through said larger section, whereby the current delivered to saidwork circuit is materially freed from fluctuations. y

5. In an ,electrical system the combination of a source of rectified alternating current, a

plurality of work circuits, and a filter' system connected between said source and said work circuits, said filter system including an induc-- tance divided into two unequal sectionslby a tap, each of said sections being connected between said source and a separate work cir-I cuit, a condenser connected betweenthe other" terminal of said source and said tap, and condensers connected between said othert'erminal and each terminal of said inductance, whereby the magnetic flux of said inductance due to the direct current component flowing to either work'circuit and alternating current component of the current flowing through -said larger inductance is materially reduced.

6. In an eleetrlcahsystem the combination Vof a source of rectified alternating current, a plurahty of work circuits, a'nd a lilter'system connected between said source and said work circuits, said filter system 'including an inductance divided into two sections with a ratio of at least Qntol by a tap, each of 'said sections being, connected between said source and a separate workrcircuit, a condenser connected between the other terminal of said. source and' said tap, and condensers connected between said other terminal and each terminal of said inductance, whereby the lmagnetic flux of said inductance due to the direct current component "flowing to either iwork circuit vand the alternating current component of the current flowing through said larger iductance is materially reduced.

`7. In an electrical system, the combina` tion of a source of rectified alternating current, a work circuit, and a' filter system conn .of said source and said tap, a capacitively reacting connection between the terminal of said larger section of said inductance and said other terminal, and a connection of substantially pure capacitive reactance between the terminal of the smaller section of said inductance and said other terminal.

. 8. In an electrical system, the combination of a source .of rectified alternating current, a work circuit, and a filter system connected between said source and said work circuit, said filter system including two unequal inductance elements coupled together, the larger only of said elements carrying direct current and being connected in the line between one terminal of said source and said work circuit, and a condenser connected across the filter' system in Series with the smaller inductance, the polarity of the mutual inductance between the inductance element-s being the same as would result from Winding both the shunt and series linductances as a single coilY and passing rectified current through -one only of the last mentioned indnctances,

whereby the alternating current component of the current flowing through said work circuit issubstantially neutralized.

9. In an electrical system, the combination of a' source of rectified alternating current,

, a work circuit, and a filter system connected between said source-and said work circuit, saidiilter system including two unequal 1nductanee elements coupled together, the

larger only of said elements carrying direct curr-ent and bemg connected 1n the line be# tween one termmal of said source and said work circuit, and a substantially pure capacitively reactive system connected across the 'filter system 1n series with the smaller 1nductance, the polarity of the mutualinductance between the inductance elements being the same as would result from winding both the shunt and series inductances as a single coil and passing rectified current through one only of the last mentioned inductances, whereby the alternating current component of the current 'flowin g ythrough said work eircuit is substantially neutralized.

10. A network for conve infr direct current from a source to a load while attenuating alternating currents which includes elements providing a series inductance, a shunting impedance including inductance and capacity arranged in series, and -a mutual inductance between the series and shunt inductances which is substantially greater than the shunt inductance and so poled that the resulting alternating magnetic fields of said inductances are opposed.

11. In a network for conveying direct current from a source to a load'while attenuating pulsating currents, a'series circuit including inductance and a shunt circuit including inductance and capacity andlmut-ual inductance between said two circuit-s having a value substantially greater than said shunt circuit inductance, said mutual inductance between said circuits being so poled that the resulting pulsating magnetic fields of said inductances are opposed.

12. A network for conveying direct current from a` source to a load while attenuating alternating currents comprising a shunt path including an inducta-ncecoil and a series path including an inductance coupled to said first named coilin such a way that the mutual inductance between said two 4coupled coils is substantially greater than the inductance of said-first-rnentioned coil, said mutual inductance being so poled that the resulting alternating magnetic fields of said inductances are opposed. y

13. In a network for conveying direct current from a source circuit to a. load circuit while attenuating alternating currents which comprises an iron-cored inductance coil and two condensers connected in series and forming an electrical circuit, one of said first two named circuits being connected to said network across one of. said condensers andthe other one' of s'aid lirst two named circuits being connected to said network across said other condenser and a predetermined portion of said coil, said portion'being such that the mutual inductance between it and the remaining portion of the coil is substantially greater than the inductance of said Iirst named portion.

In witness whereof, I have hereunto subcribed my name this 5th day of January,

BENJAMIN F. MIESSNER. 

